THE GREENHOUSE EFFECT

A PRIMER

Chapter 1

What is the Greenhouse Effect?

Earth’s Energy Sources

• The earth receives most of it’s energy from the sun.

• It also has leftover warmth from when it formed

• And it has radioactive elements decaying in it, which heats things up.

What the Earth needs

• The Earth needs to hold on to the energy from the sun and its interior for a little while

• And then it must get rid of it.• Greenhouse gases are like a blanket, in that

they insulate the Earth from the extreme heat of day and from the extreme cold of night.

• A blanket too thin leaves a planet too cold for life. One too thick boils all the water away.

The moon lacks a greenhouse effect

100ºC by day -173º C by

night

Venus suffers a runaway greenhouse effect

Read an interesting article here

Shrouded in CO2, Venus’ surface temp is about 450º

The Earth’s Greenhouse Effect is just right

H-o-o-o-o-t. B-a-a-a-a-a-a-d

T-t-t-t-oo

C-c-c-c-c-old

Just right. Ahhhhhhhhh

Earth’s Greenhouse Effect

It protects against heat AND cold

Chapter 2

Earth’s Energy Budget and the Global warming

Radiation Balance

• Averaged over several years, the amount of incoming solar radiation (insolation) that strikes the Earth (240 W/m2) exactly balances what the Earth emits back to space (terrestrial radiation, 240 W/m2 ).

• This balance results in the average temperature of Earth, which supports life as we know it.

Radiation Balance: What goes in must come out

Global Warming

• The key to understanding our life-giving climate is in understanding the rate at which the Earth sheds it energy.

• That’s what’s special about the greenhouse effect; it moderates how quickly incoming energy is lost to space.

Global Warming - natural and good!

• If the atmosphere had no greenhouse effect, the Earth would be a brisk -18º C!! Too cold!!

• Over the last 500,000 years, the Earth’s temperature has fluctuated between 19ºC and 27ºC - nice and warm and good for life.

Surface temperature vs Planet temperature

• Earth’s average surface temperature ~15C• A Reasonable assumption:

– Surface of earth radiates heat with an average temperature of 15C

• However, satellite data indicate Earth radiating heat average temperature ~-16C

• Why the discrepancy?– What accounts for the 31C heating?

Global Warming• The Earth reflects some light immediately.

The rest is absorbed by the surface of the Earth, which gets warm.

• Warm things glow. Which is to say, the warm Earth radiates this energy as infrared radiation into the air.

• Greenhouse gases absorb the 95% of this IR and give some of it back to Earth – and what stays in the atmosphere keeps it warm.

• The portion of IR energy that is reradiated down to Earth’s surface accounts for the 31C heating

• Energy radiated from the Earth(called terrestrial radiation) from elevation of about 5 km (top of clouds) averages 240 W m-2 - the same amount as comes in– Keeps Earth’s temperature in balance– Source: www.soest.hawaii.edu/GG/FACULTY/POPP/Lecture2.ppt

“Trapped” energy

• The following are graphics that show how the daily insolation is shared among the various parts of the surface and atmosphere; albedo reflects 30% of it, the rest is absorbed by the air and the surface and re-radiated as IR light.

• The energy that is re-radiated as IR light is the energy that is responsible for global warming. Pay attention to it!

http://marine.rutgers.edu/mrs/education/class/yuri/erb.html

The cause of Global Warming

Energy Balance

Chapter 3

How Greenhouses and Greenhouse Gases work

Blackbody Radiation• To understand how greenhouse gases work, we

need to understand how greenhouses work. • All warm things RADIATE energy. All radiation

is the form of electromagnetic waves. • High-temperature object radiate short waves

(visible light), low temp objects radiate long waves (infrared light).

• Low-frequency, long-wavelength radiation is called blackbody radiation. (Black because the things don’t glow in the ranges we can see - they are dark to us)

Transparency and Opacity• When light hits atoms of some material, the

energy is absorbed. • From there, the energy can take one of two paths.• Either it is transmitted as light energy, in which

case the material is transparent• Or, the light energy RESONATES with the atoms,

which causes the atoms of the material to vibrate with a very large amplitude (via constructive interference). In this case, the atoms will bash against each other and heat up; the light energy becomes “heat energy.” The material is opaque.

How greenhouses work

• Glass has a natural frequency that matches that of IR and UV light, but not visible light.

• IR and UV light cause glass atoms to vibrate a LOT, and the light energy is turned to heat.

• Glass is transparent to visible (shortwave) light waves which pass right through but opaque to longer infrared waves, which cause the glass to warm up.

Greenhouse physics• The sun is very hot; in fact, it is glowing

hot. It radiates short waves in the visible part of the spectrum which easily pass through glass (and also air molecules).

• The light is then absorbed by ground and plants and such, and they become warm.

• These warm things reradiate that energy as blackbody radiation, but, being much colder than the sun, they radiate at a longer wavelength - in the infrared part of the spectrum.

Greenhouse physics, two

• The IR light from the ground resonates with the glass atoms; glass is OPAQUE to IR radiation. As the glass warms, it will radiate that energy in all directions - some to the outside, but some energy is reradiated back inside.

• This is why greenhouses and cars and anything with glass windows will heat up inside on a sunny day.

Glass is transparent to Short-wave visible light

Glass absorbs and radiates Infrared light; then re-radiates part back inside and part to the outside

The Earth’s greenhouse effect depends on the transparency of

Air• Mostly, air is transparent to both infrared

(long) waves and visible (short) waves

• However, some gasses in the atmosphere are OPAQUE to infrared radiation.

• They act just like glass - letting the visible light in, but only letting some of the IR light out.

Energy Escapes to space

Warm Earth radiates IR light to air

Energy comes back to Earth

By DayGreenhouse gases absorb IR light energy, then re-emit it in all directions

Escapes to space

Warm Earth radiates energy to air

Comes back to Earth

By NightAll night long, IR light energy slowly leaks out of the Earth system

Greenhouse gases

• Any gas that is transparent to visible light but opaque to infrared light is a greenhouse gas.

• Carbon dioxide and water vapor are two such gasses. They constitute a TINY portion

of the air, but they play a BIG role.

This is where all the GHGs are

The problem• We know we are tinkering with the natural

balance by increasing the levels of GHGs in the atmosphere.

• We don’t know what the outcome will be. Maybe hotter. Maybe colder.

• You can’t change just one thing because Nature is a complicated place and everything’s connected.

• What we DO know is that now is good for humans.

Enhanced Greenhouse Effect - Scary!

• What we are experiencing now is an enhanced greenhouse effect due to recent human activity. This fact is not in question.

• The vast majority of climate scientists believe that the enhanced greenhouse effect (EGE) is due to the release of additional CO2 into the atmosphere as a result of burning fossil fuels.

Chapter 2

Factors affecting the Earth’s Mean Temperature

Temperature and Radiation Balance

• The equation for determining how the temperature of the earth will change (or not) is given by:

• (incoming solar radiation minus outgoing terrestrial radiation) x time / surface heat capacity, or

Insolation

• How much energy we get from the sun varies due to natural cycles

• The sun goes through an 11-year sunspot cycle. Increased solar flare activity decreases the sun’s light output.

• Cyclical changes in the Earth’s orbit can also change how much insolation we receive.

Incoming Solar Radiation• Radiation at top of Earth’s

atmosphere = 1368 W m-2

• If Earth flat disk with no atmosphere, average radiation = 1368 W m-2

• Earth 3-dimensional rotating sphere,– Area = 4r2

– Average solar heating = 1368 4 = 342 W m-2

Albedo• How much sun energy is absorbed by a surface

depends largely on how shiny, or reflective, the surface is.

• Albedo is the percentage of incoming solar radiation that is reflected rather than absorbed; reflected solar radiation divided by the incoming solar radiation = albedo. The shinier the surface, the higher the albedo.

• Snow, ice, and low-level clouds increase Earth’s albedo. Vegetation, bare earth, and cirrus clouds decrease Earth’s albedo.

Areas of high albedo

Areas of low abledo

Average Albedo

Click for more info on Albedo

• daily changes in surface albeo

• General info about albedo

Greenhouse Gases

• Major GHGs include, but are not limited to, CO2, H2O, CH4, and N2O

• All of these have both natural and man-made origins.

• Of course, we’re pumping powerful, unnatural GHGs into the atmosphere, too.

Factors Affecting Radiation Balance: Volcanoes

• By far, the biggest polluter in the state is Madame Pele.

• The volcano spews TONS of CO2 into the air each day!

• Remember: if there weren’t natural sources of GHGs, then we wouldn’t be having this discussion because there would be no life on Earth.

How all these add up

• Climate models are tough to develop because of the interconnectedness of the parts. For example:

• Warmer air and ocean leads to more cloud cover, increasing albedo, and more snowfall, increasing albedo, and temperatures drop to iceage levels. Gobal warming MIGHT lead to global cooling.

Or, • Warming oceans release vast amounts of

CO2, and global temps rise suddenly and dramatically; land ice melts, albedo decreases; temps rise even further, melting more ice; coasts are lost rising sea levels and also to hurricanes, which gain in strength and numbers; people move inland en masse and clear forest for new cities and agriculture, releasing even more carbon into the air . . . . Etc……

Chapter 3

What makes a gas a Greenhouse Gas?

Resonance

• Infrared light from terrestrial radiation just happens to match the natural frequency of some molecules, now known as Greenhouse Gases. GHGs resonate at IR frequencies.

• When IR light hits one of these molecules, the molecules absorb the energy and begin to bend and stretch; this light energy is turned into kinetic energy (temp goes up!).

Click Link for original article

• The greenhouse gas molecules are shown in the next series of figures along with the IR spectra and the bending and vibrations caused by absorbing the IR radiation. The arrows on the molecules indicate the direction of the bends and vibrations of the bonds.

• The IR spectra graphs show the wavelengths (on x axis) and the transmittance (on y axis). At 100% transmittance, no light is absorbed; the molecule is transparent and the light passes through. But at crucial wavelengths, some/most of the energy is absorbed; thus, transmittance falls.

Chapter 4

Evidence of Global Warming

Why do we think the globe is warming up?

• The following are examples of SYMPTOMS that indicate that the Earth is, in fact, warming up.

• You will be asked to do some research of your own on this topic.

Forests are drying out, dying

• Click link to see entire article published in the Christian Science Monitor

• http://features.csmonitor.com/environment/2009/01/22/us-forests-hold-new-evidence-of-global-warming/

Link to article from Lawrence Livermore Lab re: Sea Level Increases

• New research suggests that ocean temperature and associated sea level increases between 1961 and 2003 were 50 percent larger than estimated in the 2007 Intergovernmental Panel on Climate Change report. Observations that show sea levels rose by 1.5 millimeters per year in the period from 1961-2003. That equates to an approximately 2.5-inch increase in ocean levels in a 42-year span.

Your turn!

• Do a bit of research and provide further symptoms of global warming. These might include changes in natural or human environments.

• What all these symptoms add up to is called “climate change.”

Climate Change• “Climate” refers to the long-term weather scheme

of an area. When the climate changes, precipitation (rain, snow, etc) changes. This, eventually, changes everything.

• Some areas are likely to become hot and dry, others cool and wet, and still others may become entirely frozen.

• If climates in food-growing regions become seriously disrupted, expect hunger and famine.

Chapter 5

Scientific speculation as to the underlying causes of these symptoms

Ice Cores - click link for full article from Scientific American

• Researchers have recovered a nearly two-mile-long cylinder of ice from eastern Antarctica that contains a record of atmospheric concentrations of carbon dioxide (CO2) and methane--two potent and ubiquitous greenhouse gases--spanning the last two glacial periods. Analysis of this core shows that current atmospheric concentrations of CO2--380 parts per million (ppm)--are 27 percent higher than the highest levels found in the last 650,000 years.

Ice cores also show the connection between CO2 and average global

temperature (click link for details)

• Average global average temperatures have indeed been rising while atmospheric CO2 increases at a rate of approximately 1.6ppm per year

Your turn!

• Where are scientists looking to uncover the mystery of climate change?

• Hint: lake sediments store pollen samples, seabed sediments store all kinds of information, tree rings tell about rainfall patterns, amber preserves air samples from ancient times.

Chapter 6

Lights! Cameras!

ACTION!

Human’s role in the Abundance of Carbon in the Atmosphere

• Currently, much of Earth’s carbon is locked up as fossil fuels and standing trees and biomatter. These “standing carbon” sources are called carbon sinks.

• When this carbon is burned or digested, it becomes part of the air, as CO2 or as CH4

• CO2 is also stored in rocks, soil, and the ocean. These are also considered sinks. These release CO2 when heated.

Humans and Atmospheric Carbon, continued

• Burning wood, burning fossil fuels, and burning forests to create grasslands for farting cows all transform carbon sinks into atmospheric carbon.

• CO2 is a weak GHG, but we are pumping LOTS of it into the air. CH4 (methane) is a much more powerful GHG, and we are creating a lot of it through ranching and deforestation practices.

Begin with theTurn it into wood Burn to clear

land

Raise cattle on it

Transport the meat

Amazon Rainforest

CH4

CO2

CO2

Mmmmm

CO2

CARBON SINK

International Efforts to curb Global Warming

• Kyoto Protocol

• Intergovernmental Panel on Climate Change (IPCC)

• Asia-Pacific Partnership on Clean Development and Climate

Industry Efforts• Increased efficiency of power production

• Replacing the use of coal with cleaner fossil fuels (oil, natural gas)

• Use of combined heating and power systems (CHP)

• Increased use of nuclear and renewable, alternative energy sources

• CO2 capture and storage

• Hybrid/alternative cars & transportation

Individual Efforts

• Walk, bike, bus, carpool. Live near to where you work.

• Wash clothes with cold water. Take shorter showers. Line dry your clothes.

• Use CFLs instead of regular light bulbs.• Have fewer children.• Eat less feedlot beef and pork. Grow your

own food. Buy from local farmers.